I think "mentally ill" is pretty unfair. Passionate, depressed, maybe even self-righteous? Sure, all of these.

But his capacity for logic doesn't seem to be affected. English isn't his first language, but he still writes in full, grammatically correct sentences that are very clear. Wordy and emotional - yes. But not mentally ill.

I think we should be careful not to dismiss/overlook people because we don't share their emotional perspective on the world. In other words, just because he's a unique character doesn't mean his take on set theory should be ignored.

From a very brief click through (and from my own fairly superficial memory of the topic), it doesn't seem to be extremely unconventional. At the very least, it's not standing shoulder to shoulder with Timecube.

A lot of geniuses have issues. I wouldn't use this to judge the rest of his work.

The author is evidently far from neurotypical. Generally I find these kinds of diverse viewpoints interesting, if not appealing.

Unfortunately his prose borders on unreadable. There may very well be excellent ideas here, but until he follows the commandment "omit needless words" nobody is going to wade through it.